1. Field of the Invention
The present invention relates generally to a stereotaxic surgical procedure and more specifically to a stereotaxic surgical procedure for the precise placement of an instrument to a specific target region in the brain.
2. Description of Related Art
Stereotaxic surgery has conventionally been the primary method for the precise placement of instruments to specific targets within the human brain. Despite its widespread use especially in the treatment of Parkinson""s Disease, a certain margin of error in localization exists. This error may vary, for example, from 1 mm to 5 mm. Therefore, when precise localization is required, refinement of existing technology may be desired.
The present invention provides an apparatus and method for more accurately positioning instrumentation in a brain of a patient. The apparatus is straightforward in design and construction and can be used with existing technology without requiring a substantial level of increased surgical skill.
Accordingly, an apparatus for positioning instrumentation into a target region of a brain is provided, the apparatus generally comprising an attachment member adapted to be secured to a cranium of a patient and a marker assembly adapted to be connected to a locator device. The locator device may comprise, for example, a conventional stereotaxic headframe assembly, which is suitable for positioning an installation probe into a cranium of a patient based on predetermined coordinates derived, for example, from data obtained from a brain imaging scan.
In accordance with one aspect of the present invention the locator device includes a stereotaxic arc and an installation probe extending therefrom. The marker assembly generally comprises a cannula preferably made of a ceramic material. The cannula is adapted to fit over a distal portion of the installation probe such that a distal end of the cannula is closely, and preferably precisely, aligned with a distal end of the installation probe. The stereotaxic locator device is used to facilitate the insertion of the installation probe, having the cannula attached thereto, through a burr hole and into the brain such that the distal end of the installation probe and cannula are placed in close proximity of the target region to be treated. Upon being so positioned in the brain, a proximal end of the cannula is secured, preferably by an adhesive, to the attachment member in order to immobilize the cannula within the brain at the desired angular orientation.
Importantly, the marker assembly, including the cannula and a needle inserted through the cannula, is adapted to be detached and removed from the locator device after the cannula has been immobilized in the desired orientation. In one embodiment of the present invention, the needle is sized to extend at least about 5 mm to about 10 mm beyond the distal end of the cannula to the precise location of the target region. The needle preferably is formed of a carbon fiber, and may be constructed to include an indexing element or other means for determining and adjusting the effective depth of the needle into the brain in increments of less than about 5 mm, and more preferably in increments of about 1 mm or 2 mm. Advantageously, the marker assembly and attachment member have a sufficiently low surface profile, with respect to the cranium surface, to enable a surgeon to cover the wound with the scalp of the patient in order to maintain sterility of the surgical site.
The brain may then be subjected to a verification scan and imaging procedure, while the marker assembly is immobilized within the brain, in order to verify the position of the distal end of the needle with respect to the target region in the brain. Upon an optimal verification scan, the target region can then be treated by reopening the scalp and inserting a surgical device and/or treatment substance through the needle.
Notably, if the verification scan has revealed that the cannula is not at a desired orientation in the brain, the cannula and attachment member can be removed from the cranium and/or repositioned. Data and images obtained from the verification scan can be used in the calculation of new coordinates useful in the subsequent positioning of the same or another cannula.
The attachment member preferably comprises an Aluminum or other non-ferrous member, preferably a disc-shaped member including a flanged proximal portion circumscribing an aperture sized to receive the installation probe and marker assembly. Preferably, the flanged proximal portion has a diameter of between about 6 mm and about 16 mm, and has a radius of curvature approximating the radius of curvature of a human cranium. The attachment member further includes a substantially cylindrical distal protrusion depending from the flanged portion. The. substantially cylindrical distal portion is adapted to fit within the burr hole, and to be at least partially filled with an adhesive for securing the cannula proximal end to the attachment member and hence to the cranium. The inner surface of the attachment member distal portion is textured or grooved, or may include one or more channels defining reservoirs for holding cured adhesive in place.
The attachment member is secured to the cranium by means of surgical screws or the like, with the flanged portion overlaying a periphery of the burr hole. Preferably, the attachment member has a depth that is less than a thickness of the cranium to which the attachment member is secured. The depth of the attachment member is preferably less than about 10 mm, for example about 6 mm, for a cranial plate having a thickness of about 10 mm. The attachment member is structured, when at least partially filled with cured adhesive, to immobilize the cannula when the installation probe is removed from within the cannula, the cannula being immobilized at the same orientation as the distal portion of the installation probe.
In accordance with one aspect of the present invention, a method for positioning instrumentation at an exact target region of a brain is provided. The method generally comprises the steps of securing an attachment member onto a cranium of a patient, connecting a marker assembly to a locator device, which is suitable for positioning the marker assembly in the brain based on predetermined location data of the target region, and introducing the marker assembly into the brain of the patient such that a distal tip of the marker assembly is located in a vicinity of the target region of the brain. Additional steps include immobilizing the marker assembly in the brain, and removing the locator device from the marker assembly while the marker assembly is immobilized in the brain. Preferably, the step of immobilizing the marker assembly includes a step of securing the marker assembly to the attachment member. In accordance with one aspect of the present invention, the method additionally includes a step of verifying the location of the marker assembly with respect to a location of the target region of the brain. Advantageously, the step of verifying can be performed while the marker device is immobilized within the brain and a determination can be made of whether the marker device is positioned accurately.
The step of verifying can include a step of obtaining data relating to the location of the marker assembly with respect to the location of the target region. In addition, the method preferably includes, after the step of verifying, a step of introducing a surgical instrument or active agent, such as a medication, through the needle of the marker assembly to treat the target region.